Preheat oven to 220°C/gas mark 7.
In a saucepan over medium heat, cook onion, carrots, peas and celery in olive oil until soft and translucent. Add chicken and cook for 15-20 minutes. Season with salt and pepper.
Prepare a 23cm (9 inch) pie dish by lining with pastry.
Place the chicken mixture of the prepared pie dish and add grated Parmigiano Reggiano grated on the top. Cover with top pastry, seal edges and cut away excess pastry.
Bake in the preheated oven for 40-45 minutes or until pastry is golden brown.
*All information included in this recipe has been provided by Italia Formaggi.